The invention relates to an apparatus and method for controlling data writing. In particular, the invention relates to an apparatus and method for controlling data writing to a tape medium.
A drive to write data to magnetic tapes such as with LTO (Linear Tape Open) format receives synchronization commands from a host (an application program) periodically during a writing. The synchronization command is a command to force write data accumulated in a tape drive buffer to a tape medium. The application periodically sends the synchronize command to assure that all data sent to the tape drive has been written to the tape medium and does not remain in the buffer of the tape drive.
When the tape drive receives a synchronization command, the tape drive buffer becomes empty. Then, the tape drive usually performs a “backhitch.” A backhitch is a series of operations including stopping the transport of the tape medium once, rewinding the tape medium in a reversed direction, thereafter transporting the tape medium again in the original direction to the target position to restart writing the next data.
A backhitch requires approximately two or three seconds. Since the writing of next data starts after completion of this backhitch, frequent synchronization commands cause considerable degradation in write performance.
There have been proposed techniques of writing without execution of backhitch.
Japanese Patent Application Publication No. 2006-318571 describes an apparatus including a host I/F unit to store a dataset sent from a host into a buffer memory, as well as to send the dataset to the host, and a medium I/F unit to take out a dataset stored in the buffer memory and to transfer the dataset to a tape, as well as to store a dataset read from a tape into the buffer memory. The apparatus acquires a data rate with the host from the host I/F unit, acquires an error rate in writing to the tape from the medium I/F, determines a tape speed based on the data rate and the error rate, and performs control to transport the tape with the determined speed.
Japanese Patent Application Publication No. 2004-341925 describes a storage apparatus to sequentially write multiple sets of write data to a data recording medium in segment units of a predetermined size. For each of sets of write data, the storage apparatus writes the set of write data to at least one segment of the data recording medium when the set of write data is received in association with a write command to write the set of write data to the data recording medium. In the case where the size of one set of write data is smaller than a prescribed size that is determined in advance, the storage apparatus concatenates the one set of write data and multiple sets of write data written after the one set of write data, among the multiple sets of write data sequentially written to the data recording medium, and then writes the concatenated sets of write data to a smaller number of segments than the number of segments originally required to write the sets of write data targeted for the concatenation. In addition, the storage apparatus performs backhitchless flush of writing write data to a tape recording medium without executing backhitch, and thereby operates with a higher speed than in the case of executing the backhitch.
PCT International Application No. 2008-533636 discloses a helical scan tape recorder including a rotatable scanner, and a transport system for transporting a magnetic tape to a position proximate to the rotatable scanner in a manner so that information can be recorded during a revolution of the scanner. In the helical scan tape recorder, a controller performs, as a pause routine for pausing during a recording operation on the tape, the steps of: determining a tape pause position reference value indicative of a pre-pause last recording position on the tape; recording an erase signal on the tape after the pre-pause last recording position; rewinding the tape; transporting the tape in a forward direction and obtaining a current tape position value; determining when the current tape position value reaches a predetermined value relative to the tape pause position reference value; and at beginning of a next revolution of the scanner, commencing recording of one or more post-pause stripes on the tape.